Project 1. The overall goal of this project is to understand the mechanisms involved in the neurokinin-1 receptor (NK-1R), the substance P (SP) preferring receptor, antagonist-mediated anti-HIV activity in human immune cells. Our earlier studies have shown that the NK-1R antagonist (CP-96,345) inhibits HIV infection of macrophages, at least in part, through down-regulation of CCR5, a principal co-receptor for HIV entry into macrophages. In addition, CP-96,345 inhibits endogenous SP production by the immune cells. In support of these in vitro findings, we have documented that there are elevated SP levels in HIV-infected subjects in comparison to uninfected subjects, and that HIV infection induces SP expression in human immune cells. These important in vitro and in vivo data indicate the necessity of further investigation of the potential of using NK-1R antagonists as a therapeutic approach for HIV disease. In this proposal, we will extend the scope of our investigations by testing the anti-HIV ability of other NK-1R antagonists in both CD4+ T cells and macrophages infected with different strains of HIV. We will examine the mechanisms responsible for the anti-HIV activity of the NK-1R antagonists. Our overarching hypothesis is that NK-1R antagonists are potent inhibitors with both antiviral and immunomodulatory effects. We will also examine the hypothesis that the NK-1R antagonists reduce the neurotoxic effects of HIV infection and its proteins (gp120 or Tat) on the human neuronal cells. We propose new in vitro studies to determine the anti-HIV activity of NK-1R antagonists in PBMC from both normal and HIV-infected subjects (Aims 1 and 2). The impact of the NK-1R antagonists on drug-resistant HIV infection of immune cells, as well as their synergistic effect with the commonly used antiretrovirals, also will be a new focus of this proposed study (Aim 1). In conjunction with the Project 2, we will examine the mechanism(s) responsible for the anti-HIV activity of the NK-1R antagonists (Aim 3). In Aim 4, we will determine whether the NK-1R antagonists have the anti-HIV activity in microglia, the primary HIV target cells in the CNS, and whether the NK-1R antagonists have the neuroprotective effect on human neuronal cells. These studies represent a unique series of experiments directed toward elucidating the anti-HIV ability and mechanisms of the NK-1R antagonists and will provide further scientific evidence for using the NK-1R antagonists as a potential therapeutic agent for treatment of HIV disease.